1. Field of the Invention
The present invention relates to an apparatus for processing workpieces such as semiconductor wafers or liquid-crystal display (LCD) substrates, and also a method of processing such workpieces.
2. Description of the Related Art
One of the steps of manufacturing semiconductor device is to etch the surface region of a semiconductor substrate covered by a photoresist film, thereby forming a fine pattern on the substrate. After this step, it is necessary to remove from the substrate the photoresist film which has been used as an etching mask. To remove the photoresist film, so-called ashing processing has been used hitherto.
Ashing process is advantageous in that only unnecessary parts of the photoresist film can be removed from the substrate, without scratching or damaging the surface of the substrate. This process is also employed to wash masks and silicon wafers and to remove ink or residual solvent therefrom. Further, it is suitable as a dry cleaning process which is performed in manufacturing semiconductor devices.
Published Unexamined Japanese Patent Application 52-20766 discloses an ashing apparatus which applies an ozone-containing gas to the surface of a semiconductor substrate. The apparatus comprises a chamber, and an electric heater, a heating plate, and a gas distributor all located within the chamber. The electric heater is positioned below the heating plate, for heating the heating plate. The gas distributor is located above the heating plate and has nozzles when heated by the heater, the heating plates radiates heat. The heat serves to form in the chamber an ashing-gas atmosphere of 1 atmospheric pressure or lower pressure in the chamber. The gas distributor uniformly applies the ozone-containing ashing gas through its nozzles to the surface of a semiconductor water mounted on the heating plate. More precisely, the ashing gas is applied onto the photoresist film formed on the semiconductor wafer, and reacts with the photoresist which is high-molecular organic substance, causing the same to peel off the semiconductor wafer.
In recent years, larger and larger semiconductor substrates are used to manufacture semiconductor devices. For example, the LCD substrate used at present are square glass plates, each side of which is about 300 mm long. The larger the semiconductor substrates, the more important it is to apply the ashing gas uniformly to the entire surface of each substrate. Here is a problem. Since the nozzles of the gas distributor take specific positions with respect to the semiconductor substrate which is to be processed, the gas is inevitably applied to the portions of the substrate in different concentrations. Consequently, portions of the substrate undergo ashing to different degrees, in particular when the semiconductor substrate is relatively large.
In the conventional ashing apparatus, described above, an ozone-containing ashing gas is applied to a semiconductor substrate in an atmosphere of 1 atmospheric pressure or a lower pressure. The ashing gas, which contains ozone, can help to achieve ashing processing, but at a comparatively low speed. Therefore, it is generally adopted to get a high temperature at the ashing treatment or to get a high concentration of a treatment gas so as to improve the ashing treatment speed. However, these means are undesirable since the substrate material is damaged and the apparatus cost becomes high.
Various methods of processing semiconductor substrates are known. One of these methods is to apply ultraviolet rays from an ultraviolet-ray source to a semiconductor substrate placed within a CVD-gas atmosphere, thus depositing a film on the substrate. Another of these methods is to apply ultraviolet rays to a semiconductor substrate in an etching-gas atmosphere, thereby etching the surface region of the substrate. The efficiency of either method is low, and requires a huge space and a proportionally large apparatus.